Capturing CO2 from a flue gas through calcium cycling is one of the most recognized and promising carbon reduction technologies. In calcium cycling capture technology, a CaO absorbent reacts with CO2 in the flue gas to produce CaCO3 to thereby reduce the concentration of CO2 in the flue gas. A common reactor is a bubbling fluidized bed (BFB) or a circulating fluidized bed (CFB). However, a fluidized bed faces challenges with respect to large-scale applications. That is, in large-scale applications, a massive amount of gas needs to be discharged from colossal coal-fired power plants that operate on megawatt basis. Such amount of gas cannot be adequately handled by the above fluidized bed, leaving the fluidized bed an infeasible means for large-scale applications. Without an effective reactor for large-scale applications, the capture technology for processing CO2 discharged from colossal coal-fired power plants cannot be implemented, in a way that the total emission of CO2 cannot be considerably reduced.
The cement industry also accounts as one of the main sources of CO2 emission. During a combustion process in the cement industry, the concentration of CO2 in a flue gas produced from combustion is only 25 to 30 vol % due to unsatisfactory air combustion and airtightness. As a result, the cement industry also requires the CO2 capture technology for increasing the concentration of CO2 to provide reuse and storage effects. Further, the cement industry is one of the six main power consumption industries, and usually lacks a mechanism for recycling waste heat in the calcination process. Thus, the energy efficiency of the fabrication process of the cement industry is commonly low. Although the energy efficiency of the cement industry may be increased by cogeneration, e.g., producing electricity with waste heat, manufacturers of the cement industry still need to additionally invest enormous amounts of funds and installation costs for such cogeneration.